GFAAS determination of selenium after separation with thiol cotton in lichens and plants: the importance of adding a mineral matrix before decomposition

This study reports a preparation technique for the determination of Se concentration in lichens and plants, using matrix separation and preconcentration of samples with thiol cotton. Sample digestions were done using HNO3–H2O2–HF. A graphite furnace atomic absorption method has been used for the determination of Se in the different samples. The method was validated through the analysis of four certified reference materials (lichen, grass and sea lettuce) and of four in-house lichen materials. A limit of determination of 0.02 μg g−1 in the solid sample and a precision (relative standard deviation) varying from 3 to 15% was found through the course of this study. The most important finding resides in the fact that a mineral matrix must be added to the lichen and plant samples before decomposition to obtain high and constant recoveries.